globi

I know that F1 engines don't run at 6000 rpm. However power output is more or less proportional to the engine speed. I just wanted to show just because a race engine is a race engine doesn't mean that it can break the laws of physics. The torque number of an F1 engine is not much higher than of a 3.0 l production engine if both engines have the same static compression ratio.

You can always simplify to some level. If you limit displacement, rpm and static compression ratio engines will be around the same power level.
You won't find a new 2.0l engine making the same power at 4000 rpm as another new 4.0l engine if both engines have the same static compression ratio.

One of the main reason why race engines are powerful is because they can spin faster and have a higher static compression ratio.

globi

It would work if you'd run off the battery, but again it would need much more power without overlap than with overlap.
Besides you'd gain more power by running a compressor to push more fresh gases in than running a pump to suck more exhaust gases out.

A header is essentially a 'reverse turbo' just without moving parts that essentially uses the energy already in the exhaust gases to generate a reduced pressure.

tuj

The above posters are right about the compression ratio. It comes into play even more when dealing with the effective compression ratio with FI. Lower static and more boost is better than high static and low boost.

tuj

Because scavenging increases the thermal efficiency of the engine.

Yes, the but virtue of a race engine is that it can rev safely and flow at those high rpms.

globi

Have you thought about why scavenging at partial throttle should increase efficiency? If there's overlap some of the fuel can leave through the exhaust port and this would obviously reduce efficiency (which btw is not that unlikely considering the fact how close inlet and outlet valves are).
I could see efficiency improvement if it reduces pumping losses (but most engines have EGR - so this is already taken care of) or if it somehow increases turbulence in the combustion chamber and therefore lead to a more complete combustion. Both are big IFs though.

rotarygod

While this is an extreme example, it has alot of very relevant information as they are using zero overlap. read through all of the choices on the right to get an idea of how the theory works. There are several things that we wouldn't want to do but some of it could apply to the Renesis.

http://www.impulsengine.com/how/briefhow.shtml

dannobre

iTrader: (3)

Interesting read.....seems to be almost exactly opposite to a lot of conventional wisdom.

Do you think that this will help make the rotary's unique combustion chamber shape more efficient...and speed up the flame front...

TeamRX8

iTrader: (25)

kind of funny that they don't show dyno sheets etc. to back up their claims

Richard Paul

iTrader: (5)

Sounds like that thing was written for a research grant.
It'll start but that's about it.

TeamRX8

iTrader: (25)

at a minimum it would greatly sacrifice top end for low end, maybe on a low rpm poppet valve engine but I can't see it working on a wankel

globi

http://www.impulsengine.com/how/briefhow.shtml

If you could design a thing that creates incredibly low pressures, power could be increased on a 4 cycle engine (rotary and piston) but I don't see how one can exceed far more than 10% (they're mentioning double), since the dead volume as discussed before is not more than about 10% anyway.

It actually states here that it doesn't work:
Obviously when it builds up back pressure directly after the combustion chamber how can it create a vacuum in the combustion chamber? Yes, it can create a vacuum after the restriction in the exhaust pipe but how would that benefit the engine?
Btw this is called Laval nozzle (or converging diverging nozzle) and was invented about 120 years ago when they designed the first steam turbines.

Wasn't there a guy named 'Smokey' that came up with that hot air concept in the 80's? As I can imagine that it would increase mileage due to reduced pumping losses and improved combustion, I don't see how a less dense charge can increase power.

rotarygod

Obviously as I stated not all of that would be usable but some of what they discuss is quite relevent and feasible. I'm not going to go so far as to say that running a smaller exhaust pipe with no overlap and a hot air intake will give you supercharged power. The relevant issue is that you could use exhaust velocity with no overlap to get less than ambient pressures in the engine before the intake ports open. That would be very possible. It would have some effect on power.

Richard Paul

iTrader: (5)

Non of this is going to do anything for the rotary because even if you had a negative pressure in there you have no volume of it. example, what say you took the vacuume reserve for your power steering and reduced it to the size of a pill bottle, you'd have not much braking power. Because you ran out of vacuume, you used it up.

Now Smokey Yunick's engine is something I know about. Smokeys idea was homoginazation, you all know that I worked on that too. Mine was doing it with my "blender" as Smokey called it. We talked on the phone alot about this. In his application he used a turbo to homg the mixture but it didn't work well as it tosed the fuel out of mixture. He had to superheat all the ducting after the turbo to keep it mixed. He didn't know about my blower when he worked on this project.

His idea was getting it well vaporized under low load then using the turbo for high power. Problem was transition whereby shutting off the heat to all the tubing took to long. But he told me that once the fuel was mixed it stayed that way for long time without falling out. This is what I found also.

He then was quick to tell me not to bother with Detroit, I'd be beating my head against the wall. He said they don't want to hear anything not even from him.
Many years ago they would fund promising projrcts but not since the '60's have they shown any interest in outside development.
All they want now is to buy a "black box" from someone. Meaning do your own development work on your own money.

Last time I saw Smokey was at the Indy 500 in '96 or '97. At that time I showed him my then new 5 inch blower. (The new one is 4.4) He offered it to his wife for use as a goood garbage disposal. I'm not sure if that was a compliment or not.

Anyway this thread is using up to much of my time. I'm not going to comment any further on any of above. Fred if you want to discuse it call me sometime and we can go over it.

globi

Richard, thanks for elaborating about Smokey's engine. I have never read the entire story and always thought how would he have gained power when he reduced the air density by heating the intake charge, but now it's clear.

Regarding the 'negative pressure' (which is just less than atmospheric pressure):
If you reduce the pressure in the exhaust chamber more exhaust will leave through the exhaust which would then allow more combustionable mixture to enter the intake even if there's no overlap (I don't see why this concept would be not valid for all 4 cycle engines).
I definitely see the benefit of reduced pressure in the exhaust chamber, I just don't see how it could be achieved with a some 'Megaphon' pipe.

Anyway back to the header:
I'd be curious to know what the power increase with headers was on the 10A, 12A and 13B engine. This could tell us whether rotary engines actually achieved higher power with overlap (in percentage to the max power).

dannobre

iTrader: (3)

If there is exaust/intake opening overlap there will be no residual negative pressure...it will just pull intake flow into the exaust. The negative pressure " supercharging" results from the sealed -ve pressure left after the port closes...sucking in intake charge when the intake valve opens...

globi

Exactly that's why an engine with overlap is way more effective in improving filling. Only a small 'negative pressure' (this is a bad word) is needed to get better filling.

dannobre

iTrader: (3)

True...I think that overlap traditionally allows for dilution of the residual exaust gases with intake charge. I think what they are trying to say is they are getting a lot of "neg pressure" that results from "exaust flow suction" and a closed intake valve.....this would result in better scavenging and less residual exaust gas in the chamber...and better filling of the intake charge.

I can't believe though that it would work....the exaust flow wouldn't continue when there is nowhere for the flow to come from....expansion of the hot gases would only account for so much........I would really need to see this working to believe that it is this simple???

I think the Renesis zero overlap is more to do with lowering HC emissions than anything else.

I do think though that it gives credence though to stiffle the " bigger is better" header designs that result in low exuast gas flow...

What the hell do I know though...there are a lot more qualified people on here than me

tuj

Any pressure below atmospheric is a negative pressure or vacuum. Scavenging is the result of moving gases pulling other gases, either exhaust pulling the intake charge into the engine (when there is overlap) or the exhaust gas already in the header pulling the exhaust gases out of the engine.

One reason overlap is beneficial even at partial throttle, is that the intake creates a bigger vacuum at partial throttle openings, which can actually draw the residual gases back into the intake. Residuals are very harmful to torque production. Without overlap, you can't hope to get all of the residuals out of the combustion chamber. When using overlap, its better to have the exhaust closer later to increase overlap than to open the intake earlier.

The problem is that there is a distinct point at which the scavenging effect of overlap results in less residuals than no overlap. Unfortunately, that point is higher than idle, which is where most emissions are measured. Also, uncombusted fuel is worse for emissions and the cat. (ie. blowing down with overlap) than burned exhaust gases.

globi

I was cleaning up today and found a German book about rotary engines that I bought about 15 years ago and thought I lost. It has the title "Rotationskolben-Verbrennungsmotoren" and was written by W. D. Bensinger - the guy that lead the rotary engine development at Daimler-Benz (I guess this guy should have some credibility - after all he lived well before the stock option and severance package era, possibly during a time when managers actually cared about what they were working on ).
Anyway on page 75 he writes extensively about the difference between peripheral ports and side ports. He notes that due to the large overlap the incoming almost continous gas stream at full throttle, 'pushes' the exhaust gases back and therefore allows a much better filling than with side ports and less or no overlap (which is obvious since with no overlap the exhaust gases, even if pushed back, have no-where to go since the exhaust port is obviously closed). However he also notes that peripheral ports have a significant disadvantage at partial throttle; a significant amount of exhaust gases can re-enter the intake and this can lead to a misfire. If this occurs the unburnt gases get recycled and eventually ignited again which can lead to a ignition every 3rd, 6th or even 9th revolution and can lead to an unpleasant jerking during cruising (a 'phenomena' piston engines don't have to deal with).

rotarygod

Bridgeport and peripheral ports have always made more low end and midrange power than standard side port 13B engines. The key to that however is at what load. At higher loads this is true. At low loads the increased overlap kills low end power. Gas mileage suffers and the engine sputters and bucks around. Load is everything. The Renesis with it's lack of overlap makes more power everywhere than the last 13B (that has overlap). It takes some decent sized porting and overlap to make a 13B generate the power the Renesis does. Lack of overlap is apparently either misunderstood or underestimated because it seems to do very well.

TeamRX8

iTrader: (25)

yep, again it's a whole different game folks, the old rules aren't always going to apply

globi

Actually the book doesn't state anything else. However it especially points out the difference between partial and full throttle than low and high rpm.

Again what I tried to point out is that there is indeed excellent scavenging with overlap (and more so than with piston engines) and that if you have overlap a header will lead to significant power gains. Bensinger specifically states that peripheral ports with their large overlap, exhaust and intake tuning will lead to significant power gains. And frankly the 26B is a very nice example where this was proven.

And again it's not about comparing the Renesis with the 13B and whether overlap is better or not; it's about whether the Renesis can significantly benefit from a header design. So far no-one was able to come up with a header that leads to significant power gains and here's obviously a very reasonable explanation.

I'm sorry but this is simply ignorant, there is no different game. The Renesis is not a new engine concept. This design has been considered by NSU over 40 years ago already. Unfortunately materials back then weren't strong enough to allow side exhaust ports.
Mechanical design of piston and rotary engines hasn't conceptually changed during the last decades. What mainly improved engines is engine management, better materials and better tools.
There is a reason why internal combustion engine books originally printed in the 60's still sell. The internal combustion engine is about 150 years old and it doesn't deal with any thermodynamical or mechanical laws that weren't discovered over a 100 years ago already.

TeamRX8

iTrader: (25)

I know all that, you simply misunderstood my intention, some of your own comments in this thread are less than enlightening if judged on the surface, it goes back to what I said before about the Renesis not being easily modeled using the conventional techniques

globi

I'm not saying the Renesis header is easily modelable. Although it's not as complicated as some suggest as long as you strictly keep both rotors seperate (strictly divide the siamese port).
What I'm saying though is that a Renesis with header has a maximum power-gain, which is lower than what another engine with overlap would gain from a header.

TeamRX8

iTrader: (25)

well maybe I'm not so ignorant afterall, this didn't get copied over from the other thread:

https://www.rx8club.com/showpost.php...&postcount=178